Cellulose-solvent-based lignocellulose fractionation with modest reaction conditions and reagent cycling

ABSTRACT

Embodiments of the present invention overcome the well-known recalcitrance of lignocellulosic biomass in an economically viable manner. A process and system are provided for the efficient fractionation of lignocellulosic biomass into cellulose, hemicellulose sugars, lignin, and acetic acid. The cellulose thus obtained is highly amorphous and can be readily converted into glucose using known methods. Fermentable hemicellulose sugars, low-molecular—weight lignin, and purified acetic acid are also major products of the process and system. The modest process conditions and low solvent/solid ratios of some embodiments of the invention imply relatively low capital and processing costs.

FIELD OF THE INVENTION

The present invention relates to the field of pretreatment andfractionation processes for converting lignocellulosic biomass intocellulose, hemicellulose sugars, lignin, and acetic acid.

BACKGROUND OF THE INVENTION

Biorefineries could become the foundation of industrial development inthe twenty-first century. The biorefinery is similar in concept to thepetroleum refinery, except that it is based on conversion of biomassfeedstocks rather than crude oil. Biorefineries in theory can utilizemultiple forms of biomass to produce a flexible mix of products,including chemicals, fuels, power, heat, and materials.

The biorefinery concept has already proven successful in the globalagricultural and forest-products industries, where such facilities nowproduce food, feed, fiber, or chemicals, as well as heat and electricityto run plant operations. Biorefineries have long been in place in thepulp and paper industry, wherein hardwood or softwood is converted intopulp for papermaking and other uses. Currently, the high processingcosts and the narrow margin between feedstock costs and product valueare important obstacles to commercialization beyond these traditionalindustries.

The growth of the biorefining industry relies on the efficientconversion of not just wood, but many other types of lignocellulosicbiomass which are abundantly available annually. Examples of suchlignocellulosic biomass include hardwood, softwood, recycled paper,waste paper, forest trimmings, pulp and paper waste, corn stover, cornfiber, wheat straw, rice straw, sugarcane bagasse, and switchgrass.Efficient conversion includes overcoming one of the key technicalchallenges for the emerging biorefining industry: the recalcitrance ofthe cellulose contained in naturally occurring lignocellulosic biomass.Overcoming the recalcitrance of cellulose so that it can bedepolymerized to glucose is important, as glucose is a biorefineryplatform intermediate that can be fermented or reacted to a wide varietyof industrially relevant chemicals, such as ethanol, citric acid, andthe like.

Lignocellulosic biomass typically contains 35-50 wt % cellulose, 15-35wt % hemicellulose, and 5-30 wt % lignin, depending on its origin (Zhangand Lynd, 2004; Klein and Snodgrass, 1993; Wyman, 1994). Althoughcellulose, hemicellulose, and lignin are usually the major components oflignocellulosic biomass, there also exist varying amounts of othermaterials present in both bound and unbound forms. These minorcomponents include proteins, uronic acids, acetic acid, ash, free sugarssuch as sucrose, soil, and foreign materials such as metals originatingfrom harvest operations.

Cellulose is nature's most abundant polymer and is a polymer of glucose.The glucose molecules are joined by β-1,4-glycosidic linkages whichallow the glucose chains to assume an extended ribbon conformation.Hydrogen bonding between chains leads to the formation of flat sheetsthat lay on top of one another in a staggered fashion. As a result,cellulose is very chemically stable and serves as a structural componentin plant walls (Paster et al., 2003).

Hemicellulose is a polymer containing primarily 5-carbon sugars such asxylose and arabinose with some glucose and mannose dispersed throughout.Hemicellulose forms a polymer that interacts with cellulose and ligninin the plant wall, strengthening it.

Lignin helps bind the cellulose-hemicellulose matrix while addingflexibility. The molecular structure of lignin polymers is random anddisorganized and consists primarily of carbon ring structures (benzenerings with methoxyl, hydroxyl, and propyl groups) interconnected bypolysaccharides.

The recalcitrance of lignocellulosic biomass is believed to be caused by(i) the complicated linkages among several mainpolysaccharides—cellulose, hemicellulose, and lignin, which restrict thehydrolysis action of cellulases, hemicellulases, and laccases; and (ii)the inherent properties of cellulosic material—low substrateaccessibility to cellulases, high degree of polymerization, and poorsolubility of cellulose fragments in water (Zhang and Lynd, 2004). Thelignin-hemicellulose matrix encases cellulose and prevents access ofcellulase enzymes to the cellulose phase. Cellulose and hemicellulose innative lignocellulosic biomass are only slightly digestible by cellulaseand hemicellulase enzymes.

Pretreatment of lignocellulosic biomass has been an actively researchedfield for several decades, and a wide variety of thermal, mechanical,and chemical pretreatment approaches (and combinations thereof) havebeen investigated and reported in the scientific literature (McMillan,1994). The objective of pretreatment, historically, has been to break upthe linkages among cellulose, hemicellulose, and lignin by removinglignin and/or hemicellulose, to produce enzymatically digestiblecellulosic solids. The aim has been to maximize conversion ofcarbohydrate polymer to the desired monomer while minimizing the loss ofthe desired monomer to degradation products.

Modem pretreatment approaches have evolved from traditionalthermochemical biomass-hydrolysis processes that were developed prior toWorld War II (McMillan, 1994). These processes typically employedcooking of biomass with an acid catalyst (often hydrochloric or sulfuricacid) in a pressurized reactor to hydrolyze the cellulose fraction ofbiomass to glucose. In such processes, yields of glucose are typicallyno higher than about 60%, as the harsh conditions required for cellulosehydrolysis result in a significant fraction of the released glucosebeing converted to non-fermentable sugar degradation products such as5-hydroxymethylfurfural. In addition, single-stage processes designedfor cellulose hydrolysis resulted in the loss of pentose carbohydrates(C₅ sugars) from the hemicellulose fraction.

The discovery of cellulase enzymes and the subsequent development of anindustrial cellulase industry, coupled with the availability ofefficient pentose-fermenting microorganisms, have dramatically alteredthe way in which the pretreatment of biomass is approached. Rather thanrequiring a thermochemical process to hydrolyze cellulose to glucose,the aim of many pretreatment approaches is to produce a solid substratein which the cellulose can be efficiently digested (depolymerized toglucose) by cellulase enzymes.

Pretreatment of lignocellulosic biomass is often the most costly step inan overall conversion process, and it impacts the cost of most otheroperations including the reduction in size of the feedstock prior topretreatment, as well as enzymatic hydrolysis and fermentation afterpretreatment. Pretreatment can be strongly associated with downstreamcosts involving enzymatic hydrolysis, power consumption, productconcentration, detoxification of inhibitors, product purification, powergeneration, waste-treatment demands, and other process operations(Wooley et al., 1999; Wyman et al., 2005).

Intensive lignocellulose-pretreatment efforts have been undertakenduring the past several decades, but current technologies have not yetbeen commercialized on a large scale due to high processing costs andgreat investment risks (Wyman et al., 2005). Many pretreatmenttechnologies employ severe reaction conditions resulting in degradationof sugars and formation of inhibitors, and generally high processingcosts.

In general, there is good agreement in the art that amorphous celluloseis more digestible than crystalline cellulose. Hydrolysis of amorphouscellulose requires less catalyst and shorter reaction time, and hashigher sugar yields, as compared with that of crystalline cellulose.Amorphous cellulose can be regarded as a homogenous substrate with atleast an order of magnitude higher reaction rate than that ofcrystalline cellulose hydrolysis by acids (Fengel and Wegener, 1984) orcellulose enzymes (Zhang and Lynd, 2005).

A review of the pretreatment art (Chang and Holtzapple, 2000) found thatthe enzymatic reactivity of lignocellulosic biomass correlates mostclosely with lignin content and cellulose crystallinity, which bothrelate to the accessibility of the cellulose. It is therefore recognizedthat an efficient lignocellulosic-biomass pretreatment process comprisesdecrystallizing part of the cellulose, rendering it amorphous, as wellas removing some of the lignin from the starting material. It is alsodesired to fractionate the biomass such that hemicellulose sugars andacetic acid can be recovered.

What is needed is an efficient pretreatment and/or fractionationtechnology for lignocellulosic biomass, wherein cellulose isdecrystallized, lignin is substantially removed and recovered,hemicellulose sugars are substantially removed and recovered, andwherein the process conditions for performing the reactive separation donot degrade the extracted sugars or produce appreciable quantities ofinhibitors for downstream fermentation.

Another economic obstacle for the fractionation of lignocellulosicbiomass is that large quantities of solvent are generally required,leading to high capital and operating costs for the plant. Therefore,what is needed is a process that can achieve the benefits characterizedabove, using relatively low quantities of solvent, such as solvent/solidratios of about 5 or less.

It is further desirable that such an efficient pretreatment and/orfractionation technology would be flexible for a variety of biomassfeedstocks and co-product options, and would require modest processconditions so as to be economical.

SUMMARY OF THE INVENTION

The present invention addresses several needs in the art, includingutilization of all major components of lignocellulosic biomass byfractionating and recovering cellulose, hemicellulose, lignin, andacetic acid; the production of highly amorphous cellulose which can bereadily converted into glucose; and efficient solvents allowing modestprocess conditions that translate to relatively low capital andoperating costs.

In some embodiments of the invention, a process for the fractionation oflignocellulosic biomass is provided. Some embodiments of the inventionteach solvent combinations that are effective for fractionatinglignocellulosic biomass. Some embodiments of the present inventiondescribe highly reactive amorphous cellulose that can be produced andthereafter readily converted into glucose for fermentation or otheruses. Some embodiments of the invention provide a system for thefractionation of lignocellulosic biomass into cellulose, hemicellulose,lignin, and acetic acid.

Embodiments of the invention can be described by the following processsteps, which also relate to elements of a system of the invention:

Step (i) provides lignocellulosic biomass, which can be for examplehardwood, softwood, recycled paper, waste paper, forest trimmings, pulpand paper waste, corn stover, corn fiber, wheat straw, rice straw,sugarcane bagasse, or switchgrass. The lignocellulosic biomass may havebeen modified prior to step (i). For example, reduction of particlesize, washing, modifying the moisture content, or conditioning may havebeen performed on part or all the feedstock before subjecting to theprocess and system of the present invention.

Step (ii) combines a first solvent with the lignocellulosic biomass,dissolving some, preferably at least 50%, more preferably at least 90%,and most preferably substantially all of the cellulose and hemicellulosepresent.

Step (iii) combines a second solvent with the material from step (ii),precipitating some, preferably at least 50%, more preferably at least90%, and most preferably substantially all of the amorphous celluloseand dissolved hemicellulose, and extracting some, preferably at least50%, and more preferably at least 75% of the lignin.

The first solvent comprises one or more chemicals selected from thegroup consisting of hydrochloric acid, sulfuric acid, nitric acid,phosphoric acid, polyphosphoric acid, acetic acid, sulfur dioxide, zincchloride, sodium hydroxide, potassium hydroxide, ammonia, lithiumchloride/N,N-dimethylacetamide, 1-butyl-3-methylimidazoliumhexafluorophosphate, dimethylsulfoxide/tetrabutylammonium fluoridetrihydrate, N-methylmorpholine-N-oxide, cadmium monoxide/ethylenediamine(cadoxen), and water. In some preferred embodiments, the first solventcomprises polyphosphoric acid.

The second solvent comprises one or more chemicals selected from thegroup consisting of methanol, ethanol, 1-propanol, 2-propanol, acetone,propanal, 1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water. In some preferred embodiments, the second solventcomprises acetone.

In some embodiments, the invention further comprises the followingsteps:

Step (iv) combines a third solvent (which may be the same as ordifferent than the second solvent) with the material from step (iii) towash the first solvent and lignin from the solid amorphous cellulose,and then separates the solid phase from the black liquor. In somepreferred embodiments, this third solvent also comprises acetone, toreduce the complexity of downstream solvent recovery.

Step (v) combines a fourth solvent, which preferably comprises water,with the solid phase from step (iv) to wash the second and/or thirdsolvents and hemicellulose sugars from the solid amorphous cellulose,and then separates the solid phase from the light liquor.

In some embodiments, the invention further comprises the followingsteps, which need not necessarily be performed in sequential order:

Step (vi) separates the black liquor into the first solvent, the secondsolvent, and/or the third solvent, a lignin-rich liquid, and aceticacid. Preferably, removal of the second and/or third solvent reduces thelignin solubility such that lignin precipitates, thereby increasing theefficiency of step (vii) that follows.

Step (vii) recovers low-molecular-weight lignin from the lignin-richliquid in step (vi).

Step (viii) separates the light liquor into soluble hemicellulose sugarsand one or more of the second solvent, the third solvent, and the fourthsolvent.

Step (ix) further recovers the first solvent from a process streamexiting step (viii). The recovered solvent can be stored or recycled foruse in step (ii).

Various secondary steps may be desirable to further purify or otherwisetreat the solvents prior to recycling them back into the process orsystem.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a block-flow diagram representing several embodiments ofthe fractionation process for lignocellulosic biomass, according to thepresent invention.

FIG. 2 depicts a process-flow diagram representing one illustrativeembodiment of the fractionation process and system for corn stover,according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the process of the present invention, lignocellulosic biomass isfractionated into cellulose, hemicellulose sugars, lignin, and aceticacid. “Lignocellulosic biomass” can be a wide variety of materials, suchas hardwood, softwood, recycled paper, waste paper, forest trimmings,pulp and paper waste, corn stover, corn fiber, wheat straw, rice straw,sugarcane bagasse, switchgrass, and mixtures of one or more types oflignocellulosic biomass. One skilled in the art will recognize thatother cellulose-containing feedstocks exist and can be fractionated bypracticing the methods of the present invention.

In general, the lignocellulosic biomass is in the form of a particulate,but particle size is not regarded as critical. Particle-size reductionmay be performed in conjunction with the methods of the invention, inorder to provide convenient processing of solid lignocellulosic biomass.

As used herein, “fractionation” means the removal of at least somecellulose from a lignocellulosic-biomass feedstock. “Pretreatment” meansthat the cellulose phase of the lignocellulosic biomass is modified insome way, such as a change in crystallinity, degree of polymerization,surface area, binding to hemicellulose and/or lignin, and solubility ina certain solvent.

As used herein, “amorphous cellulose” means the disrupted physical stateof the cellulose molecules while in solution and for that period of timeafter precipitation and before reversion to the highly orderedcrystalline structure associated with native cellulose. As is wellknown, when in such amorphous state, cellulose is much more readilyhydrolyzable compared to the crystalline, native state.

Separation of “substantially all” of a component from a startingmaterial means that the amount of the component remaining in thestarting material is such that its concentration is at or below thedetection limit of standard analytical techniques. Detection limits canbe 1% or less, depending on the component and the technique.

Unless otherwise indicated, all numbers expressing concentrations ofcomponents, reaction conditions, separation conditions, and so forthused in the specification and claims are to be understood as beingmodified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending at least upon the specific analytical technique. Thenumerical values set forth are reported as precisely as possible. Anynumerical value, however, inherently contains certain errors necessarilyresulting from the standard deviation found in their respective testingmeasurements.

The invention can be understood by reference to the block-flow diagramin FIG. 1, which depicts several embodiments but is not intended tolimit the scope of the claimed invention. These embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that modifications tothe various disclosed embodiments may be made, and other embodiments maybe utilized, without departing from the spirit and scope of the presentinvention. The following detailed description is, therefore, not to beregarded as limiting in any way. Furthermore, some embodiments of thepresent invention encompass fewer than all of the described steps, as isdescribed herein. Also, steps (iv)-(ix) are not necessarily sequential.

Step (i) provides lignocellulosic biomass.

Step (ii) combines a first solvent with the lignocellulosic biomass,dissolving some of the cellulose and hemicellulose present. The solventmay comprise some catalytic activity to moderately hydrolyze celluloseand hemicellulose into small fragments, as further described below.

Step (iii) combines a second solvent with the material from step (ii),precipitating some of the amorphous cellulose and dissolvedhemicellulose, and extracting some of the lignin.

Step (iv) combines a third solvent with the material from step (iii) towash the first solvent and some lignin from the solid amorphouscellulose, and then separates the solid phase from the black liquor.

Step (v) combines a fourth solvent with the solid phase from step (iv)to wash the second and/or third solvents and some hemicellulose sugarsfrom the solid amorphous cellulose, and then separates the solid phasefrom the light liquor.

Step (vi) separates the black liquor into the first solvent, the secondsolvent, and/or the third solvent, a lignin-rich liquid, and aceticacid. Preferably, removal of the second and/or third solvent reduces thelignin solubility such that lignin precipitates, thereby increasing theefficiency of step (vii) that follows.

Step (vii) recovers low-molecular-weight lignin from the lignin-richliquid in step (vi).

Step (viii) separates the light liquor into soluble hemicellulose sugarsand one or more of the second solvent, the third solvent, and the fourthsolvent.

Step (ix) further recovers the first solvent from a process stream fromstep (viii).

The following description will enable a person of ordinary skill in theart to practice the present invention.

According to FIG. 1, lignocellulosic biomass is provided in step (i).One skilled in the art of biomass pretreatment or fractionation willrecognize that there are a number of possible preparation proceduresthat can be performed on the lignocellulosic biomass feedstock, prior tothe reactor in step (ii). Some examples of preparation include reductionof particle size through grinding, milling, chopping, and the like;washing to remove soil and/or other foreign particles; modifying themoisture content of the solids; and conditioning such as through certainstorage conditions. The desirability to use such preparation procedures(and others) will depend on the type and source of the lignocellulosicbiomass, the choice of downstream equipment, and to some extent on thedesired product mix. The economic-optimum process conditions forsubsequent steps will sometimes depend on how the feedstock is prepared,but it does not require undue experimentation to understand theinfluence of feedstock preparation on fractionation efficiency,according to the methods of the present invention.

In any of steps (ii)-(v), the reactor or separator (“vessel”) cangenerally be a continuously stirred tank, a continuous tubular reactor,or a batch tank. Any vessel can work provided there is a means formoving solid and liquid material into and out of the system (and in thecase of step (ii), means for a vapor stream). The vessel contents arepreferably mixed to some extent, in order to reduce mass-transferlimitations between the solvent and the solid phase, and to enhance therate of approach towards phase equilibrium. Materials of constructionare chosen based on the selected solvent and process conditions, and thedesired flexibility for the particular vessel. In general, specialvessels are not necessary due to the modest process conditions forpracticing this invention.

In step (ii), lignocellulosic biomass and a first solvent are fed to areactor. The first solvent for step (ii) is selected so as to dissolvesome of the cellulose present in the starting solid phase. By “cellulosesolvent” is meant a liquid that is able to penetrate thecellulose-hemicellulose-lignin matrix and dissolve cellulose, which canoccur by several mechanisms. One possible mechanism, for example,relates to swelling the cellulose and providing the solvent access tothe crystalline cellulose molecules. However, swelling does notnecessarily lead to dissolution; likewise, dissolution can occur withoutswelling per se. “Cellulose dissolution” by a cellulose solventcomprises a transition from a two-phase system to a one-phase system, inwhich the original supramolecular structure of cellulose is destroyed(Klemm et al., 1998). Other mechanisms for dissolution relate toreversible chemical reactions between the solvent and thecellulose-hemicellulose-lignin matrix. The solvent may contain catalyticactivity such that at least one of its components is able to break uplinkages among cellulose, hemicellulose, and lignin, and/or is able tomoderately hydrolyze cellulose and/or hemicellulose into smallfragments. In some embodiments, hemicellulose is hydrolyzed in step (ii)such that the hemicellulose oligomers possess good solubility in water,which tends to increase the efficiency of separation in step (v), ifpresent. The amorphous cellulose and cellulose oligomers will notgenerally have good solubility in water, which allows for cleanseparation (if desired) of cellulose and hemicellulose in step (v).

Preferably, the first solvent dissolves at least 50%, at least 60%, atleast 70%, at least 80%, at least 90%, at least 95%, at least 98%, atleast 99%, or more, of the cellulose present. Most preferably, the firstsolvent dissolves substantially all of the cellulose present. In someembodiments, the first solvent also dissolves at least 50%, at least60%, at least 70%, at least 80%, at least 90%, at least 95%, at least98%, at least 99%, or more, of the hemicellulose present.

The solvent for cellulose (“first solvent”) comprises one or morechemicals selected from the group consisting of hydrochloric acid,sulfuric acid, nitric acid, phosphoric acid, polyphosphoric acid, aceticacid, sulfur dioxide, zinc chloride, sodium hydroxide, potassiumhydroxide, ammonia, lithium chloride/N,N-dimethylacetamide,1-butyl-3-methylimidazolium hexafluorophosphate,dimethylsulfoxide/tetrabutylammonium fluoride trihydrate,N-methylmorpholine-N-oxide, cadmium monoxide/ethylenediamine (cadoxen),and water. Effective concentrations will depend at least on the specificsolvent(s) selected.

One particularly effective solvent for cellulose is polyphosphoric acid.The following discussion describes features associated withpolyphosphoric acid, which is the cellulose solvent (first solvent) forsome embodiments of the present invention. Similar features foracid-containing solvents other than polyphosphoric acid will berecognized by a skilled artisan.

By “polyphosphoric acid” it is meant concentrated phosphoric acid, suchthat any number of polymers of phosphoric acid may be present insolution. Phosphoric acid (also known as orthophosphoric acid) is acommon tribasic acid, H₃PO₄, having three replaceable hydrogen atoms.When two phosphoric acid molecules are condensed into one molecule,pyrophosphoric acid (H₄P₂O₇) is obtained as follows:

2H₃PO₄→H₄P₂O₇+H₂O

This process can be repeated to increase the average degree ofpolymerization of the phosphoric acid present. Polyphosphoric acidmolecules can have dozens of such phosphoric units bonded in a row. Ageneral formula for polyphosphoric acid is HO(PO₂OH)_(x)H where x is thenumber of phosphoric units in the molecule. Any concentrated solutionwill have a distribution of degrees of polymerization. Polyphosphoricacid imparts catalytic activity towards hydrolysis of cellulose andhemicellulose during step (ii), and the specific activity is a functionof the degree of polymerization.

The phosphoric acid units can be bonded together in cyclic structuresforming metaphosphoric acid molecules. The simplest such compound istrimetaphosphoric acid or cyclotriphosphoric acid, H₃P₃O₉.

The third —OH group on a polyphosphoric acid repeat unit can also beused for condensation with other phosphoric groups to form branches inthe polyphosphoric acid chains. The cyclic four-phosphate unit thatdouble-branches, to remove all water, creates phosphoric anhydride,P₄O₁₀, which is often written empirically as P₂O₅. P₂O₅ is also theoxidized phosphorous compound that is produced by burning (or otherwiseoxidizing) solutions of phosphoric acid or polyphosphoric acid, as forexample during solvent-recovery operations. Although P₂O₅ is notformally a proton donor, for the purposes of the present invention P₂O₅is considered to be a phosphoric compound belonging to “polyphosphoricacid” Polyphosphoric acid is water-soluble. In aqueous solutions, waterwill hydrolyze polyphosphoric acid into smaller units and finally intomonomeric phosphoric acid (H₃PO₄), given enough water. The rate at whichthe solution approaches the equilibrium distribution of molecularweights by hydrolysis will depend on at least temperature and pH. Hightemperature and low pH tend to cause faster hydrolysis.

In polyphosphoric acid, any number of the somewhat acidic —OH groups inthem can dissociate to become negatively charged oxygen sites, formingnumerous combinations of multiple-charged polyphosphate anions. In anaqueous solution, the degree of dissociation will depends on the pH.Polyphosphoric acid can form polyphosphates by replacing one or moreavailable hydrogen atoms with one or more other positive ions. Salts oresters of polyphosphates can then be formed, depending on which cationsare present in the reactor.

As is known, lignocellulosic biomass may contain various salts andbuffering components that can contribute cations to the solution. Someexamples of polyphosphate salts that can be produced in step (ii) arecalcium phosphate, Ca₃(PO₄)₂; monobasic calcium phosphate, Ca(H₂PO₄)₂;dibasic calcium phosphate, CaHPO₄; tribasic calcium phosphate,Ca₃(PO₄)₂; ammonium phosphate, (NH₄)₂HPO₄; sodium hexametaphosphate,Na₆P₆O₁₈; and oligomers thereof. Generally, the concentration ofpolyphosphate salts will be minor, and their presence does notnecessarily decrease the efficiency of step (ii) or any downstreamoperations. For the purpose of the present invention, “polyphosphoricacid” is meant to include the various polyphosphate salts that can alsobe formed.

Without being limited by any particular theory, cellulose dissolution inpolyphosphoric acid involves two main processes: (1) an esterificationreaction between alcoholic hydroxyl groups of cellulose andpolyphosphoric acid to form cellulose polyphosphate, and (2) acompetition of hydrogen-bond formation between hydroxyl groups ofcellulose chains and hydrogen-bond formation between one hydroxyl groupof a cellulose chain and a water molecule or with a hydrogen ion.Cellulose polyphosphate reversibly converts back to free polyphosphoricacid and amorphous cellulose without any significant substitution andrecrystallization. Polyphosphoric acid dissolves cellulose rapidly andat low temperatures, in part because of the fast diffusivity of thehydrogen ions from polyphosphoric acid into the heterogeneous cellulosephase. The regenerated cellulose remains amorphous and has highreactivity.

The second solvent for step (iii) is selected principally so as toprecipitate at least 50%, at least 60%, at least 70%, at least 80%, atleast 90%, at least 95%, at least 98%, at least 99%, or more, of theamorphous cellulose present in the mixture produced in step (ii). Mostpreferably, the second solvent precipitates substantially all of theamorphous cellulose. The precipitation is believed to be caused by areduction in solubility of dissolved cellulose such that phaseseparation occurs, wherein a solid phase containing amorphous cellulosecan be recovered.

In some embodiments, the second solvent also precipitates at least 50%,at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, atleast 98%, at least 99%, or more, of the dissolved hemicellulose presentin the mixture produced in step (ii).

In some embodiments, the second solvent also dissolves some lignin thatis present in the mixture. Dissolving lignin into the solvent duringstep (iii) will lead to cellulose and hemicellulose of higher purity,which is believed to be advantageous for conversion to glucose andhemicellulose sugars downstream, and will increase the amount of ligninthat can be recovered during step (vii) below. Preferably, the secondsolvent extracts into the liquid phase at least 50%, at least 60%, atleast 70%, at least 80%, at least 90%, at least 95%, at least 98%, atleast 99%, or more, of the lignin present in the lignocellulosicbiomass. Most preferably, 75% or greater of the total lignin in thestarting material is dissolved during step The second solvent for step(iii) comprises one or more chemicals selected from the group consistingof methanol, ethanol, 1-propanol, 2-propanol, acetone, propanal,1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water. During step (iii), any number of differentchemicals may be added sequentially, but the second solvent willcomprise at least one of these chemicals.

One skilled in the art will recognize that other solvents exist thathave the desired properties for step and that selection of the secondsolvent may be impacted by the choice of the first solvent in step (ii).The second solvent is preferably volatile so that it can be recoveredeconomically in steps (vi) and/or (viii). However, the second solventneed not have any particular volatility, as long as it is effective forprecipitating cellulose and hemicellulose and for dissolving lignin.

The third solvent for step (iv), if present, is selected so as toprovide a means of washing the amorphous cellulose of the first solvent,the second solvent, and lignin. As is known, significant delignification(removal of lignin) can occur during washing steps after pretreatment,because mechanical forces (for any solvent) and/or thermodynamic drivingforces (for solvents that dissolve lignin) favor the removal of looselybound lignin from the cellulose into the solvent phase. The thirdsolvent comprises one or more chemicals selected from the groupconsisting of methanol, ethanol, 1-propanol, 2-propanol, acetone,propanal, 1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water. In preferred embodiments, the third solvent is thesame as the second solvent, but it need not be. For example, the thirdsolvent could comprise hot water, removing some lignin by primarilymechanical forces, such as would be experienced during simplefiltration.

The fourth solvent for step (viii), if present, is selected primarily tosolubilize the hemicellulose sugars (monomers and/or oligomers).Examples of hemicellulose sugars that could be present include xylose,arabinose, galactose, mannose, and glucose (hemicellulose often containssome glucan, which is the main component of cellulose). The fourthsolvent should also be able to wash other residual solvents from theamorphous cellulose. The residual solvents are one or more of the firstsolvent, the second solvent, and the third solvent. An aqueous solutionis a preferred fourth solvent because hemicellulose sugars are generallywater soluble, and especially when the previous solvents in the processare water-soluble. The fourth solvent preferably comprises one or morematerials selected from the group consisting of liquid water, steam,recycle water, process condensate, fermentation-broth condensate, andcarbon dioxide.

The quantity of solvents used throughout the process, relative to thequantity of total lignocellulosic biomass, has a significant impact onprocess economics, as is well known. In the present invention, theeffective solvent concentration for any step will depend to some extentat least on solvent type, temperature, pH, residence time, and equipmentconfiguration.

By “solvent/solid ratio” is meant the mass ratio of total solventpresent divided by the total mass of the solid phase present in aparticular step. If the step comprises a continuous separation, e.g. afixed bed of solids through which passes a liquid solvent, then thesolvent/solid ratio is calculated by dividing the total mass of solventfed in one residence time by the total mass of solids treated in thatsame residence time.

In step (ii), the solvent/solid ratio for the first solvent is less thanabout 10, preferably less than about 5, more preferably less than about3, and most preferably about 2.

In step the solvent/solid ratio for the second solvent is less thanabout 50, preferably less than about 20, more preferably less than about10, and most preferably less than about 5.

In step (iv), the solvent/solid ratio for the third solvent is less thanabout 50, preferably less than about 20, more preferably less than about10, and most preferably less than about 5.

In step (viii), the solvent/solid ratio for the fourth solvent is lessthan about 100, preferably less than about 50, more preferably less thanabout 20, and most preferably less than about 10.

In preferred embodiments of the present invention, severe reactortemperatures are not necessary. The temperature in step (ii) can beambient temperature (about 25° C.), or it can be from about 20° C. toabout 80° C. A preferable temperature for step (ii) is about 50° C.Temperatures for all other steps of the present invention can also befrom about 20° C. to about 80° C. During any of the steps, thetemperature may change (intentionally or otherwise). The specifictemperatures for any process steps are not regarded as critical, andoperating outside of about 20-80° C. should not necessarily be construedas representing an embodiment that is outside the scope of the presentinvention. As is known, however, excessive temperatures will often causeundesirable side reactions, such as hydrolysis of sugar oligomers;degradation of soluble sugars to e.g. furfural or hydroxymethylfurfural;and reactions forming complexes among sugars, lignin, and solvents.

The pH is another process parameter usually of interest. The pH in anyof the steps of the invention is not limited to any particular range,because the performance criteria can be met for many different solvents(with wide-ranging pKa values). The pH of the liquid phase willinfluence the kinetics of side reactions, beyond the effect oftemperature, but the low temperatures as taught above translate intoprocess flexibility with regards to pH. In some embodiments, the pH instep (ii) is between about 1 and about 2, and the pH values in steps(iii)-(v) are between about 4 and about 8. In other embodiments, the pHvalues will be different.

The residence times of the various steps are also not regarded ascritical, provided that the intended function is accomplished. Again,the low temperatures reduce the necessity for tight control of reactor(or separator) residence times. For purposes of illustration and tocompletely enable the present invention, in some embodiments theresidence times of the individual steps (ii)-(v) are between about 5minutes and about 4 hours, preferably about 30 minutes, chosen simplyfor convenience.

Most preferably, each step is optimized to be just long enough toaccomplish a nearly uniform distribution of the contents and to achievephase equilibrium, so that separation/washing is most effective. Longertimes would be wasteful from an overall plant-capacity standpoint, butthey would not generally limit the effectiveness of the biomassfractionation. As is appreciated in the process industries, flexibilitywith residence times or batch times of various unit operations isimportant to mitigate process upsets and ultimately provide a robustmanufacturing plant.

The pressures of the various steps of the invention are also flexible.For convenience, all pressures are chosen to be approximately 1 bar.Pressures that are too low could cause solvent losses, while highpressures usually translate into more-expensive equipment. Preferably,the pressures are chosen to be from about 0.1 bar to about 2 barthroughout the process of the invention. Higher pressures may benecessary for certain solvents that are volatile and for highertemperatures (i.e., near 80° C.). Most preferably, all steps areoperated at or close to atmospheric pressure.

Beyond the characteristics discussed above that can produce highlyreactive amorphous cellulose, an economically viablelignocellulosic-biomass fractionation process must recycle its solvents,and must recover usable hemicellulose sugars and lignin. Steps (vi)-(ix)are intended to recover solvents, hemicellulose sugars, acetic acid, andlignin.

In step (vi), the black liquor from step (iv) is fed to a separationunit operation selected from the group consisting of distillation,single-stage evaporation (flash), multiple-effect evaporation,thermocompression, and venturi scrubbing. In preferred embodiments, adistillation column is employed, the column provided with enough stagessuch that substantially pure second solvent (or a combination of secondand third solvents, if they are different) can be withdrawn. Thewithdrawal is preferably near the top of the column if the secondsolvent is a low-boiling solvent, such as acetone. This recovered secondsolvent can then be stored in a tank, or recycled back into the processat steps requiring that solvent.

Additionally, the first solvent, or a stream containing the firstsolvent, can be withdrawn directly from the separator in step (vi). Insome preferred embodiments wherein step (vi) comprises a distillationcolumn and wherein the first solvent is polyphosphoric acid, a materialstream can be withdrawn near the bottom of the column. This stream couldbe recycled directly back to step (ii), but preferably, is sent to afurnace or other means for oxidation, wherein the exit stream comprisesH₂O (steam), CO₂, and P₂O₅.

Recovering the polyphosphoric acid in this way presents severaladvantages that can be realized in various embodiments. First, anoxidation step significantly purifies the first solvent and can beaccomplished in high yields. Second, the ratio of P₂O₅ to steam can beadjusted prior to recycling to step (ii), modifying the averagemolecular weight, and thus properties, of the polyphosphoric acidsolvent. Third, the concentration of P₂O₅ can be adjusted based on themoisture content of the incoming biomass from step (i), since therecovered and recycled P₂O₅ will react with the water in the biomassfeedstock to produce polyphosphoric acid. Fourth, the energy content ofthe steam from this recovery step is recovered in step (ii) when it isdesired to heat the contents of the reactor. Fifth, feeding the recycledfirst solvent as a vapor stream of water and P₂O₅, rather than liquidpolyphosphoric acid, is advantageous because mass transfer of thesolvent into the solid phase will be faster. Finally, it is possible tofully utilize all of the chemicals from the oxidative recovery, since inaddition to P₂O₅/H₂O being recycled to step (ii), the CO₂ could berecycled to the washing operation in step (v).

Also in step (vi), acetic acid is recovered from the separation unit. Inembodiments that use distillation, acetic acid can be withdrawn directlyfrom the column. Depending on the desired use for the acetic acid,further purification outside of step (vi) may be necessary.

Removing one or more solvents for lignin in step (vi) will reduce thelignin solubility such that lignin precipitates. A liquid containingprecipitated lignin can be withdrawn from the separator in step (vi),which in the case of a distiller will usually be near the bottom of thecolumn. The lignin-rich liquid could be used directly (such as forenergy generation). Alternately, it can be fed to a solid/liquidseparation operation in step (vii) wherein liquid is removed andreturned to step (vi), and the solid comprises low-molecular-weightlignin. The solid/liquid separator is preferably a centrifuge, but itcan also be a filtration device, electrostatic separator, adsorption orabsorption column, or any other means for separating liquids fromsolids. The low-molecular-weight can further be dried if desired.

In step (viii), the light liquor from step (v) is fed to a separationunit operation selected from the group consisting of distillation,single-stage evaporation (flash), multiple-effect evaporation,thermocompression, and venturi scrubbing. In some embodiments, theseparator for step (viii) is a flash tank wherein the vapor comprisesrecovered solvent and the liquid comprises soluble hemicellulose sugars.In other embodiments, a distillation column is employed, such columnprovided with enough stages such that at least one solvent can bewithdrawn (near the top of the column if one of the solvents is alow-boiling solvent, such as acetone). The column can also be designedin order to withdraw several different solvents. These recoveredsolvents can be stored in tanks, or recycled back into the process atsteps requiring those particular solvents.

The soluble hemicellulose sugars from step (viii) can be used directly,for example by feeding into a fermentor to produce ethanol; can bestored in tanks or by other means; or can be used for other purposes. Aliquid stream comprising the first solvent can also be withdrawn fromthe step-(viii) separator, and fed to a solid/liquid separation unit instep (ix) wherein liquid is removed and returned to step (viii), and thesolid comprises the first solvent. The solid/liquid separator ispreferably a centrifuge, but it can also be a filtration device or anyother means for separating liquids from solids. The first solvent can becombined with the recovered first solvent from step (vi), or otherwiserecovered and recycled.

Although several vessel-specific process parameters described herein arenot critical to define the metes and bounds of the invention, oneskilled in the art knows that there will be certain preferablecombinations of these parameters, in order to provide an economicalprocess for fractionating biomass. Optimizing the conditions of thedistinct steps is best done by optimizing the entire process, which caninvolve process modeling and simulation, testing of various conditionsrelative to the feedstock selected, understanding the influence ofcertain site-specific criteria, and the like.

By practicing the methods of the invention, lignocellulosic biomass isfractionated into amorphous cellulose, hemicellulose sugars, lignin, andacetic acid. In preferred embodiments, the product yields are high.“Yield” is the mass of a certain product recovered, divided by thetheoretical maximum based on the amount present in the initiallignocellulosic biomass (accounting for water addition to hydrolyzecellulose and hemicellulose). “Net yield,” as used herein, is calculatedas the mass of a product divided by the mass of starting feedstock. Inorder to arrive at such a number, one simply needs to multiply theyields by the mass fraction of the component of interest in the initialfeedstock. For example, 50% yield of lignin from a starting feedstockthat is 30 wt % lignin would mean a net yield of 15% (e.g., 150 kglignin per metric ton biomass feedstock).

In some embodiments, the yield of amorphous cellulose is at least 80%,at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, atleast 98%, at least 99%, or more. The amorphous cellulose can further behydrolyzed into glucose in some embodiments, wherein the yield ofglucose is at least 80%, at least 85%, at least 90%, at least 95%, atleast 96%, at least 97%, at least 98%, at least 99%, or more. In someembodiments, the yield of hemicellulose sugars is at least 70%, at least75%, at least 80%, at least 85%, at least 90%, at least 95%, at least96%, at least 97%, at least 98%, at least 99%, or more. In someembodiments, the yield of lignin is at least 50%, at least 60%, at least70%, at least 80%, at least 90%, at least 95%, at least 98%, at least99%, or more. In some embodiments, the yield of acetic acid is at least70%, at least 75%, at least 80%, at least 85%, at least 90%, at least95%, at least 96%, at least 97%, at least 98%, at least 99%, or more.

Some embodiments of the invention relate to use of a process or a systemcomprising certain steps to fractionate lignocellulosic biomass intocellulose, hemicellulose sugars, lignin, and acetic acid. Use of afractionation process or system comprises the following elements:

(i) Use of lignocellulosic biomass.

(ii) Use of a first solvent, dissolving some of the cellulose andhemicellulose present in the lignocellulosic biomass.

(iii) Use of a second solvent, precipitating some of the amorphouscellulose and dissolved hemicellulose from element (ii), and extractingsome of the lignin.

(iv) Use of a third solvent to wash the first solvent and some ligninfrom the solid amorphous cellulose.

(v) Use of a fourth solvent to wash the second and/or third solvents andsome hemicellulose sugars from the solid amorphous cellulose.

(vi) Use of a means for separating the black liquor into the firstsolvent, the second solvent, and/or the third solvent, a lignin-richliquid, and acetic acid.

(vii) Use of a means for recovering low-molecular-weight lignin from thelignin-rich liquid in element (vi).

(viii) Use of a means for separating the light liquor into solublehemicellulose sugars and one or more of the second solvent, the thirdsolvent, and the fourth solvent.

(ix) Use of a means for recovering the first solvent from a process orsystem stream from element (viii).

Some embodiments of the invention relate to use of a combination ofsolvents, wherein a first solvent is selected from the group consistingof hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid,polyphosphoric acid, acetic acid, sulfur dioxide, zinc chloride, sodiumhydroxide, potassium hydroxide, ammonia, lithiumchloride/N,N-dimethylacetamide, 1-butyl-3-methylimidazoliumhexafluorophosphate, dimethylsulfoxide tetrabutylammonium fluoridetrihydrate, N-methylmorpholine-N-oxide, and cadmiummonoxide/ethylenediaminc (cadoxen); and a second solvent is selectedfrom the group consisting of methanol, ethanol, 1-propanol, 2-propanol,acetone, propanal, 1-butanol, 2-butanol, butanal, butanone (methyl ethylketone), t-butanol, and water.

Some embodiments of the present invention further comprise use of thefractionated and recovered products—amorphous cellulose, hemicellulosesugars, lignin, and acetic acid. These four products can be used, invarious embodiments of the invention, in at least the following ways.

The amorphous cellulose obtained is highly reactive and can readily beconverted, or saccharified, to glucose monomers with either celluloseenzymes or with an acid such as sulfuric acid. The glucose can then befermented into a wide range of industrial products, including ethanol,acetone, organic acids, baker's yeast, or any other product of cellularmetabolism of the chosen microorganism for fermentation. As is known inthe art, amorphous cellulose can also be directly fermented to productsdirectly by microorganisms, without prior enzymatic or acidicsaccharification to glucose.

Likewise, the hemicellulose sugars can be fermented. The profile ofhemicellulose sugars will depend on the specific type of feedstock. Forexample, if the feedstock is hardwood chips or corn stover, thepredominant hemicellulose sugar will be xylose. Hemicellulose sugars canalso be fermented into ethanol, acetone, organic acids, baker's yeast,or any other product of cellular metabolism of the chosen microorganismfor fermentation. The hemicellulose sugars can be combined with theglucose from the amorphous cellulose and fermented together, orfermented separately. Other commercial products that can be manufacturedfrom hemicellulose sugars include feed additives for animals; xylitol,which can be used as a sweetener, and furfural, which has many usesincluding solvents as well as production of Nylon 6 and Nylon 6,6.

The lignin that is obtained is a high-quality, relatively pure,low-molecular-weight lignin that does not contain sulfur. Lignin can beburned for energy production. Some other potential applications forlignin include carbon-fiber production, asphalt production, and as acomponent in biopolymers. Persons of ordinary skill in the biomass artwill appreciate that there are a large number of potential uses of thelignin that is produced by various embodiments of the present invention.

The acetic acid recovered can be sold or further purified. Acetic acidis an important industrial chemical that is used in the production ofpolyethylene terephthalate, cellulose acetate, and polyvinyl acetate.Diluted acetic acid is often used in descaling agents; in the foodindustry, acetic acid is used as an acidity regulator. There is a largeglobal demand for acetic acid, and the ability to capture value from theacetyl groups contained in lignocellulosic biomass is expected tocontribute to the economic viability of biorefining using the methods ofthe present invention.

Embodiments of the present invention can be further understood withreference to the following aspects. By “aspect” it is meant a process, amethod, a system, a composition, a use of, and/or a use for theinvention.

Aspect 1. A process for fractionating lignocellulosic biomass, theprocess comprising:

(i) Providing lignocellulosic biomass;

(ii) Providing a first solvent and combining with the lignocellulosicbiomass, wherein the first solvent dissolves at least some of thecellulose present in the lignocellulosic biomass; and

(iii) Providing a second solvent and combining with the material fromstep (ii), wherein at least some of the cellulose that is dissolved bythe first solvent in step (ii) precipitates out of the liquid phase.

Aspect 2. The process of aspect 1, wherein the cellulose thatprecipitates in step (iii) has reduced crystallinity compared to thecellulose provided in step (i).

Aspect 3. The process of aspect 2, wherein the cellulose thatprecipitates in step (iii) is at least 90% amorphous.

Aspect 4. The process of aspect 1, wherein the second solvent extractsinto the liquid phase at least 50% of the lignin present in thelignocellulosic biomass.

Aspect 5. The process of aspect 1, wherein the second solvent extractsinto the liquid phase at least 75% of the lignin present in thelignocellulosic biomass.

Aspect 6. The process of aspect 1, wherein during step (ii), the firstsolvent dissolves at least 50% of the cellulose present in thelignocellulosic biomass.

Aspect 7. The process of aspect 1, wherein during step (ii), the firstsolvent dissolves at least 90% of the cellulose present in thelignocellulosic biomass.

Aspect 8. The process of aspect 1, wherein during step (ii), the firstsolvent dissolves substantially all of the cellulose present in thelignocellulosic biomass.

Aspect 9. The process of aspect 1, wherein during step (ii), the firstsolvent dissolves at least 50% of the hemicellulose present in thelignocellulosic biomass.

Aspect 10. The process of aspect 1, wherein during step (ii), the firstsolvent dissolves at least 90% of the hemicellulose present in thelignocellulosic biomass.

Aspect 11. The process of aspect 1, wherein during step (ii), the firstsolvent dissolves substantially all of the hemicellulose present in thelignocellulosic biomass.

Aspect 12. The process of aspect 1, wherein during step (ii), the firstsolvent dissolves at least 90% of the hemicellulose present in thelignocellulosic biomass and dissolves at least 90% of the cellulosepresent in the lignocellulosic biomass.

Aspect 13. The process of aspect 1, wherein during step (iii), thesecond solvent precipitates at least 50% of the dissolved cellulose.

Aspect 14. The process of aspect 1, wherein during step (iii), thesecond solvent precipitates at least 90% of the dissolved cellulose.

Aspect 15. The process of aspect 1, wherein during step (iii), thesecond solvent precipitates substantially all of the dissolvedcellulose.

Aspect 16. The process of aspect 1, wherein during step (iii), thesecond solvent precipitates at least 50% of the dissolved hemicellulose.

Aspect 17. The process of aspect 1, wherein during step (iii), thesecond solvent precipitates at least 90% of the dissolved hemicellulose.

Aspect 18. The process of aspect 1, wherein during step (iii), thesecond solvent precipitates substantially all of the dissolvedhemicellulose.

Aspect 19. The process of aspect 1, wherein during step (iii), thesecond solvent precipitates at least 90% of the dissolved cellulose andprecipitates at least 90% of the dissolved hemicellulose.

Aspect 20. The process of aspect 1, wherein during step the secondsolvent: precipitates at least 90% of the dissolved cellulose;precipitates at least 90% of the dissolved hemicellulose; and extractsinto the liquid phase at least 75% of the lignin present in thelignocellulosic biomass.

Aspect 21. The process of aspect 1, further comprising converting thecellulose that precipitates out of the liquid phase in step (iii) intoglucose monomers and/or oligomers.

Aspect 22. The process of aspect 21, wherein converting the cellulose toglucose comprises enzymatic reactions.

Aspect 23. The process of aspect 21, wherein converting the cellulose toglucose comprises acid hydrolysis.

Aspect 24. The process of aspect 1, further comprising recovering andrecycling at least one of the solvents back to steps (ii) and/or (iii).

Aspect 25. The process of aspect 1, wherein steps (ii) and (iii) areconducted at one or more temperatures of from about 20° C. to about 80°C.

Aspect 26. The process of aspect 1, wherein steps (ii) and (iii) areconducted at one or more pressures of from about 0.1 bar to about 2 bar.

Aspect 27. The process of aspect 1, wherein the residence times of steps(ii) and (iii) are each from about 5 minutes to about 4 hours.

Aspect 28. The process of aspect 1, wherein one or both of steps (ii)and (iii) are conducted continuously, semi-continuously, orpseudo-continuously.

Aspect 29. The process of aspect 1, wherein one or both of steps (ii)and (iii) are conducted in batches.

Aspect 30. The process of aspect 1, wherein the first solvent in step(ii) comprises one or more chemicals selected from the group consistingof hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid,polyphosphoric acid, acetic acid, sulfur dioxide, zinc chloride, sodiumhydroxide, potassium hydroxide, ammonia, lithiumchloride/N,N-dimethylacetamide, 1-butyl-3-methylimidazoliumhexafluorophosphate, dimethylsulfoxide/tetrabutylammonium fluoridetrihydrate, N-methylmorpholine-N-oxide, cadmium monoxide/ethylenediamine(cadoxen), and water.

Aspect 31. The process of aspect 1, wherein the second solvent in step(iii) comprises one or more chemicals selected from the group consistingof methanol, ethanol, 1-propanol, 2-propanol, acetone, propanal,1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water.

Aspect 32. The process of aspect 31, wherein at least two chemicals areadded in step (iii) in a sequential manner, the chemicals selected fromthe group consisting of methanol, ethanol, 1-propanol, 2-propanol,acetone, propanal, 1-butanol, 2-butanol, butanal, butanone (methyl ethylketone), t-butanol, and water.

Aspect 33. The process of aspect 30, wherein the first solvent in step(ii) comprises polyphosphoric acid.

Aspect 34. The process of aspect 31, wherein the second solvent in step(iii) comprises acetone.

Aspect 35. The process of aspect 31, wherein the second solvent in step(iii) comprises water.

Aspect 36. The process of aspect 32, wherein the second solventcomprises acetone and water.

Aspect 37. The process of aspect 30 or 33, wherein the solvent/solidratio for step (ii) is less than about 5.

Aspect 38. The process of aspect 37, wherein the solvent/solid ratio forstep (ii) is less than about 3.

Aspect 39. The process of aspect 37, wherein the solvent/solid ratio forstep (ii) is less than about 2.

Aspect 40. A process for fractionating lignocellulosic biomass, theprocess comprising:

(i) Providing lignocellulosic biomass;

(ii) Providing a first solvent and combining with the lignocellulosicbiomass, wherein the first solvent dissolves at least some of thecellulose present in the lignocellulosic biomass;

(iii) Providing a second solvent and combining with the material fromstep (ii), wherein at least some of the cellulose that is dissolved bythe first solvent in step (ii) precipitates out of the liquid phase;

(iv) Providing a third solvent and combining with the material from step(iii), and then separating the substantially solid phase and blackliquor; and

(v) Providing a fourth solvent and combining with the substantiallysolid phase from step (iv), and then separating the solid phase andlight liquor.

Aspect 41. The process of aspect 40, wherein the first solvent in step(ii) comprises one or more chemicals selected from the group consistingof hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid,polyphosphoric acid, acetic acid, sulfur dioxide, zinc chloride, sodiumhydroxide, potassium hydroxide, ammonia, lithiumchloride/N,N-dimethylacetamide, 1-butyl-3-methylimidazoliumhexafluorophosphate, dimethylsulfoxide/tetrabutylammonium fluoridetrihydrate, N-methylmorpholine-N-oxide, cadmium monoxide/ethylenediamine(cadoxen), and water.

Aspect 42. The process of aspect 40, wherein the second solvent in step(iii) comprises one or more chemicals selected from the group consistingof methanol, ethanol, 1-propanol, 2-propanol, acetone, propanal,1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water.

Aspect 43. The process of aspect 40, wherein the third solvent in step(iv) comprises one or more chemicals selected from the group consistingof methanol, ethanol, 1-propanol, 2-propanol, acetone, propanal,1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water.

Aspect 44. The process of aspect 40, wherein the fourth solvent fromstep (v) comprises one or more materials selected from the groupconsisting of liquid water, steam, recycle water, process condensate,fermentation-broth condensate, and carbon dioxide.

Aspect 45. The process of aspect 40, further comprising subjecting theblack liquor, obtained in step (iv), to step (vi), a vapor/liquidseparation operation selected from the group consisting of distillation,single-stage evaporation (flash), multiple-effect evaporation,thermocompression, and venturi scrubbing.

Aspect 46. The process of aspect 45 wherein step (vi) comprisesdistillation.

Aspect 47. The process of aspect 45 or 46, wherein acetic acid isrecovered.

Aspect 48. The process of aspect 45 or 46, further comprising recoveringat least one solvent selected from the group consisting of the firstsolvent, the second solvent, the third solvent, and the fourth solvent.

Aspect 49. The process of aspect 48, further comprising recycling atleast one of the recovered solvents to one or more of steps (ii)-(v).

Aspect 50. The process of aspect 45 or 46, wherein at least one of therecovered solvents is polyphosphoric acid.

Aspect 51. The process of aspect 45 or 46, wherein at least one of therecovered solvents is acetone.

Aspect 52. The process of aspect 45 or 46, wherein both polyphosphoricacid and acetone are recovered.

Aspect 53. The process of aspect 45, further comprising step (vii), asolid/liquid separation operation selected from the group consisting ofa centrifuge, a filtration device, an electrostatic separator, anadsorption column, and an absorption column.

Aspect 54. The process of aspect 53, wherein step (vii) comprises acentrifuge.

Aspect 55. The process of aspect 53 or 54, wherein lignin is recovered.

Aspect 56. The process of aspect 40, further comprising subjecting thelight liquor, obtained in step (v), to step (viii), a vapor/liquidseparation operation selected from the group consisting of distillation,single-stage evaporation (flash), multiple-effect evaporation,thermocompression, and venturi scrubbing.

Aspect 57. The process of aspect 56 wherein step (viii) comprises aflash tank.

Aspect 58. The process of aspect 56 or 57, wherein hemicellulose sugarsare recovered.

Aspect 59. The process of aspect 56 or 57, further comprising recoveringat least one solvent used in a different step.

Aspect 60. The process of aspect 59, further comprising recycling atleast one of the recovered solvents to one or more of steps (iii)-(v).

Aspect 61. The process of aspect 59 or 60, wherein at least one of therecovered solvents is acetone.

Aspect 62. The process of aspect 56, further comprising step (ix), asolid/liquid separation operation selected from the group consisting ofa centrifuge, a filtration device, an electrostatic separator, anadsorption column, and an absorption column.

Aspect 63. The process of aspect 62, wherein step (ix) comprises acentrifuge.

Aspect 64. The process of aspect 62 or 63, further comprising recoveringthe first solvent.

Aspect 65. The process of aspect 64, further comprising recycling thefirst solvent to step (ii).

Aspect 66. The process of aspect 40, wherein steps (ii)-(v) are eachconducted at one or more temperatures of from about 20° C. to about 80°C.

Aspect 67. The process of aspect 40, wherein steps (ii)-(v) are eachconducted at one or more pressures of from about 0.1 bar to about 2 bar.

Aspect 68. The process of aspect 40, wherein the residence times ofsteps (ii)-(v) are each from about 5 minutes to about 4 hours.

Aspect 69. The process of aspect 40, wherein steps (ii)-(v) are eachconducted continuously, semi-continuously, or pseudo-continuously.

Aspect 70. The process of aspect 40, wherein steps (ii)-(v) are eachconducted in batches.

Aspect 71. The process of aspect 41, wherein the first solvent in step(ii) comprises polyphosphoric acid.

Aspect 72. The process of aspect 42, wherein the second solvent in step(iii) comprises acetone.

Aspect 73. The process of aspect 42, wherein the second solvent in step(iii) comprises water.

Aspect 74. The process of aspect 41 or 71, wherein the solvent/solidratio for step (ii) is less than about 5.

Aspect 75. The process of aspect 41 or 71, wherein the solvent/solidratio for step (ii) is less than about 3.

Aspect 76. The process of aspect 41 or 71, wherein the solvent/solidratio for step (ii) is less than about 2.

Aspect 77. The process of aspect 40, further comprising converting thecellulose that precipitates out of the liquid phase in step (iii) intoglucose monomers and/or oligomers.

Aspect 78. The process of aspect 77, wherein converting the cellulose toglucose comprises enzymatic reactions.

Aspect 79. The process of aspect 77, wherein converting the cellulose toglucose comprises acid hydrolysis.

Aspect 80. The process of any of aspects 21-23 and 77-79, furthercomprising fermenting some of the glucose.

Aspect 81. The process of aspect 80, wherein one of the fermentationproducts is ethanol.

Aspect 82. The process of aspect 80, wherein one of the fermentationproducts is acetone.

Aspect 83. The process of aspect 1 or 40, further comprising fermentingsome of the amorphous cellulose directly.

Aspect 84. The process of aspect 83, wherein one of the fermentationproducts is ethanol.

Aspect 85. The process of aspect 83, wherein one of the fermentationproducts is acetone.

Aspect 86. The process of any of the preceding aspects, wherein thelignocellulosic biomass in step (i) is selected from the groupconsisting of hardwood, softwood, recycled paper, waste paper, foresttrimmings, pulp and paper waste, corn stover, corn fiber, wheat straw,rice straw, sugarcane bagasse, switchgrass, and mixtures thereof.

Aspect 87. The process of aspect 86, wherein step (i) comprises one ormore feedstock modifications selected from the group consisting ofreduction of particle size, washing, modifying the moisture content, andconditioning.

Aspect 88. A process for fractionating lignocellulosic biomass, theprocess comprising:

(i) Providing lignocellulosic biomass;

(ii) Providing polyphosphoric acid and combining with thelignocellulosic biomass, wherein the polyphosphoric acid dissolves atleast 90% of the cellulose present in the lignocellulosic biomass;

(iii) Providing acetone and combining with the material from step (ii),wherein at least 90% of the cellulose that is dissolved by thepolyphosphoric acid in step (ii) precipitates out of the liquid phase;

(iv) Providing acetone and combining with the material from step andthen separating the substantially solid phase and black liquor; and

(v) Providing water and combining with the substantially solid phasefrom step (iv), and then separating the solid phase and light liquor.

Aspect 89. The process of aspect 88, further comprising separating theblack liquor and recovering polyphosphoric acid.

Aspect 90. The process of aspect 89, wherein recovering polyphosphoricacid comprises burning a process stream and recycling P₂O, and steamback to step (ii).

Aspect 91. The process of aspect 88, further comprising recoveringacetone from the black liquor, the light liquor, or both.

Aspect 92. The process of any of aspects 1-91, wherein the yield ofglucose is at least 80%.

Aspect 93. The process of aspect 92, wherein the yield of glucose is atleast 90%.

Aspect 94. The process of aspect 92, wherein the yield of glucose is atleast 95%.

Aspect 95. The process of any of aspects 1-91, wherein the yield ofhemicellulose sugars is at least 70%.

Aspect 96. The process of aspect 95, wherein the yield of hemicellulosesugars is at least 80%.

Aspect 97. The process of aspect 95, wherein the yield of hemicellulosesugars is at least 85%.

Aspect 98. The process of any of aspects 1-91, wherein the yield oflignin is at least 50%.

Aspect 99. The process of aspect 98, wherein the yield of lignin is atleast 75%.

Aspect 100. The process of any of aspects 1-91, wherein the yield ofacetic acid is at least 80%.

Aspect 101. The process of aspect 100, wherein the yield of acetic acidis at least 90%.

Aspect 102. The process of any of aspects 1-91, wherein concurrently:the yield of glucose is at least 90%; the yield of hemicellulose sugarsis at least 80%; the yield of lignin is at least 50%; and the yield ofacetic acid is at least 80%.

Aspect 103. The process of any of aspects 1-91, wherein concurrently:the yield of glucose is at least 95%; the yield of hemicellulose sugarsis at least 90%; the yield of lignin is at least 75%; and the yield ofacetic acid is at least 90%.

Aspect 104. A solvent combination for fractionating lignocellulosicbiomass, the solvent combination comprising:

A first solvent selected from the group consisting of hydrochloric acid,sulfuric acid, nitric acid, phosphoric acid, polyphosphoric acid, aceticacid, sulfur dioxide, zinc chloride, sodium hydroxide, potassiumhydroxide, ammonia, lithium chloride/N,N-dimethylacetamide,1-butyl-3-methylimidazolium hexafluorophosphate,dimethylsulfoxide/tetrabutylammonium fluoride trihydrate,N-methylmorpholine-N-oxide, and cadmium monoxide/ethylenediamine(cadoxen); and

A second solvent selected from the group consisting of methanol,ethanol, 1-propanol, 2-propanol, acetone, propanal, 1-butanol,2-butanol, butanal, butanone (methyl ethyl ketone), t-butanol, andwater.

Aspect 105. The solvent combination of aspect 104, wherein the firstsolvent comprises polyphosphoric acid.

Aspect 106. The solvent combination of aspect 104, wherein the secondsolvent comprises acetone.

Aspect 107. The solvent combination of aspect 104, wherein the firstsolvent comprises polyphosphoric acid and the second solvent comprisesacetone.

Aspect 108. The solvent combination of any of aspects 104-107, whereinthe first solvent comprises at least two chemicals selected from thegroup consisting of hydrochloric acid, sulfuric acid, nitric acid,phosphoric acid, polyphosphoric acid, acetic acid, sulfur dioxide, zincchloride, sodium hydroxide, potassium hydroxide, ammonia, lithiumchloride/N,N-dimethylacetamide, 1-butyl-3-methylimidazoliumhexafluorophosphate, dimethylsulfoxidel tetrabutylammonium fluoridetrihydrate, N-methylmorpholine-N-oxide, and cadmiummonoxide/ethylenediamine (cadoxen).

Aspect 109. The solvent combination of aspect 108, wherein one of thechemicals selected for the first solvent is sulfur dioxide.

Aspect 110. The process of aspect 30 or 41, wherein the first solventcomprises polyphosphoric acid and sulfur dioxide.

Aspect 111. Amorphous cellulose produced according to the process of anyof aspects 1-103, wherein the amorphous cellulose can be hydrolyzed intoglucose or fermented directly.

Aspect 112. A system for fractionating lignocellulosic biomass, thesystem comprising:

(a) A means for separately containing a first solvent and a secondsolvent;

(b) A reaction vessel wherein the first solvent is combined with thelignocellulosic biomass, and wherein the first solvent dissolves atleast 90% of the cellulose present in the lignocellulosic biomass;

(c) A precipitation vessel wherein the second solvent is combined withthe material from vessel (b), and wherein at least 90% of the cellulosethat is dissolved by the first solvent in vessel (b) precipitates out ofthe liquid phase; and

(d) A means for recovering the precipitated amorphous cellulose.

Aspect 113. The system of aspect 112, wherein the first solvent invessel (b) comprises one or more chemicals selected from the groupconsisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoricacid, polyphosphoric acid, acetic acid, sulfur dioxide, zinc chloride,sodium hydroxide, potassium hydroxide, ammonia, lithiumchloride/N,N-dimethylacetamide, 1-butyl-3-methylimidazoliumhexafluorophosphate, dimethylsulfoxide/tetrabutylammonium fluoridetrihydrate, N-methylmorpholine-N-oxide, cadmium monoxide/ethylenediamine(cadoxen), and water.

Aspect 114. The system of aspect 112, wherein the second solvent invessel (c) comprises one or more chemicals selected from the groupconsisting of methanol, ethanol, 1-propanol, 2-propanol, acetone,propanal, 1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water.

Aspect 115. The system of any of aspects 112-114, further comprising (e)a means for recovering the first solvent, the second solvent, or both.

Aspect 116. The system of aspect 115, wherein the first solventcomprises polyphosphoric acid and the second solvent comprises acetone.

Aspect 117. The system of aspect 112 or 115, further comprising (f) ameans for recovering hemicellulose sugars, acetic acid, or lignin.

The present invention will now be further described in the followingexample which is illustrative of one preferred embodiment of theinvention and should not be considered as limiting the invention in anyway.

Example

FIG. 2 shows a simplified process-flow diagram for the present exampleof continuous fractionation of corn stover into amorphous cellulose,hemicellulose sugars, lignin, and acetic acid, according to the methodsof the invention. The first solvent is polyphosphoric acid(“Poly(H₃PO₄)” in the diagram), the second and third solvents areacetone, and the fourth solvent is water.

Corn stover (at about 50 wt % moisture) is fed into a pretreatmentreactor (the “digestor”) along with recycled polyphosphoric acid, whichis present in the digester at about 86 wt % H₃PO₄ (equivalent). Theratio of solvent to solids in the digester is about 5. The mixture isallowed to react at about 50° C. for approximately 30 minutes (residencetime) under atmospheric pressure. No heat input is needed during thisstep because mixing of concentrated acid with water is a weaklyexothermic reaction. The polyphosphoric acid not only breaks linkagesamong lignin, hemicellulose, and cellulose, but also dissolveselementary cellulose fibrils and hemicellulose. A small amount ofhydrolysis of large polysaccharides into small fragments occurs.

In the “precipitation tank,” acetone is added to precipitate dissolvedcellulose and hemicellulose into insoluble amorphous forms, and toextract solvent-soluble lignin. The solvent/solids ratio in theprecipitation tank is about 10. The temperature and pressure in theprecipitation tank are approximately ambient, and the residence time isabout one hour.

In the unit operation “washer 1” (a tank) in FIG. 2, more acetone is fedin order to remove more than 99% of the polyphosphoric acid present aswell as the solvent-soluble lignin from the solids. The liquid phaseexiting washer 1 is called “black liquor” and contains polyphosphoricacid, acetone, acetic acid, and dissolved lignin. The temperature andpressure in washer 1 are approximately ambient, and the residence timeis about 30 minutes.

In “washer 2” (a tank), water is fed in order to wash residual acetone,residual polyphosphoric acid, and water-soluble (low-molecular-weight)hemicellulose oligosaccharides from the solid amorphous cellulose. Theliquid stream exiting washer 2 is called “light liquor” and containswater, acetone, soluble hemicellulose sugars, and a trace amount ofpolyphosphoric acid. The solid phase contains primarily regeneratedamorphous cellulose. The temperature and pressure in washer 2 areapproximately ambient, and the residence time is about 30 minutes.

The solvent-recovery system in this example includes the “distiller” (adistillation column), the “flash tank,” the “furnace,” “centrifuge 1,”and “centrifuge 2.”

In the distiller, the black liquor containing polyphosphoric acid,acetone, solvent-soluble lignin, and acetic acid is separated along withregeneration of polyphosphoric acid and lignin centrifugation. Acetoneand acetic acid are separated easily after distillation and thencondensation. With the removal of acetone, the dissolved lignin isprecipitated because it has poor solubility in acidic water. Theprecipitated lignin is separated by centrifugation and drying. In thebottom of the distiller, concentrated polyphosphoric acid containingsmall amounts of sugars and extractives from the corn stover isregenerated by feeding the bottoms to a furnace. The bottoms arecompletely burned to produce a mixture containing P₂O₅, which isrecycled to the digester where it forms concentrated polyphosphoricacid. The overall process recovery of polyphosphoric acid is high, suchthat little or no fresh polyphosphoric acid needs to be added to thedigester. (For continuous operation over long periods of time, smallmake-up polyphosphoric acid may become necessary.)

In the flash tank, the light liquor containing acetone, water, somepolyphosphoric acid, and soluble hemicellulose sugars is separated byflashing and centrifugation followed by regeneration. A small amount ofCaCO₃ is added to neutralize the weakly acidic liquid and generate aprecipitate, Ca₃(PO₄)₂. Just enough CaCO₃ is added so that at about 99%of the PO₄ ³⁻ is present in the solid phase. Ca₃(PO₄)₂ is separated bycentrifugation (centrifuge 2), and then is regenerated to concentratedpolyphosphoric acid by adding concentrated sulfuric acid, as iswell-known in the phosphoric acid industry. Acetone is recycled to aholding tank by flashing and then condensing the vapors. The liquidphase from the bottom of the flash tank is pH-neutral and containswater-soluble hemicellulose sugars.

Scanning electron microscopy shows that essentially no fibrillarcellulose remains in the amorphous-cellulose product. The amorphouscellulose is further fed to the “hydrolysis tank” along with celluloseenzymes. The product from the hydrolysis tank is a solution of glucose,which is fed to the “fermentor” wherein ethanol is produced. FIG. 2indicates that some of the amorphous cellulose can generally be diverteddirectly into the fermenter, but in this example all of the amorphouscellulose is sent to the hydrolysis tank. The reactivity of theamorphous cellulose is such that nearly 97% cellulose digestibility isobtained in a standard digestibility assay (24-hour saccharificationtime using a Trichoderma enzyme loading of 15 FPU/g glucan at 50° C. and10 g glucan per liter solution).

REFERENCES

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1. A process for fractionating lignocellulosic biomass, the processcomprising: (i) Providing lignocellulosic biomass; (ii) Providing afirst solvent and combining with the lignocellulosic biomass, whereinthe first solvent dissolves at least some of the cellulose present inthe lignocellulosic biomass; and (iii) Providing a second solvent andcombining with the material from step (ii), wherein at least some of thecellulose that is dissolved by the first solvent in step (ii)precipitates out of the liquid phase.
 2. The process of claim 1, whereinthe cellulose that precipitates in step (iii) has reduced crystallinitycompared to the cellulose provided in step (i).
 3. The process of claim2, wherein the cellulose that precipitates in step (iii) is at least 90%amorphous. 4-20. (canceled)
 21. The process of claim 1, furthercomprising converting the cellulose that precipitates out of the liquidphase in step (iii) into glucose monomers and/or oligomers. 22.(canceled)
 23. (canceled)
 24. The process of claim 1, further comprisingrecovering and recycling at least one of the solvents back to steps (ii)and/or (iii). 25-28. (canceled)
 29. The process of claim 1, wherein oneor both of steps (ii) and (iii) are conducted in batches.
 30. Theprocess of claim 1, wherein the first solvent in step (ii) comprises oneor more chemicals selected from the group consisting of hydrochloricacid, sulfuric acid, nitric acid, phosphoric acid, polyphosphoric acid,acetic acid, sulfur dioxide, zinc chloride, sodium hydroxide, potassiumhydroxide, ammonia, lithium chloride/N,N-dimethylacetamide,1-butyl-3-methylimidazolium hexafluorophosphate,dimethylsulfoxide/tetrabutylammonium fluoride trihydrate,N-methylmorpholine-N-oxide, cadmium monoxide/ethylenediamine (cadoxen),and water.
 31. The process of claim 1, wherein the second solvent instep (iii) comprises one or more chemicals selected from the groupconsisting of methanol, ethanol, 1-propanol, 2-propanol, acetone,propanal, 1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water.
 32. (canceled)
 33. The process of claim 30,wherein the first solvent in step (ii) comprises polyphosphoric acid.34. The process of claim 31, wherein the second solvent in step (iii)comprises acetone. 35.-39. (canceled)
 40. A process for fractionatinglignocellulosic biomass, the process comprising: (i) Providinglignocellulosic biomass; (ii) Providing a first solvent and combiningwith the lignocellulosic biomass, wherein the first solvent dissolves atleast some of the cellulose present in the lignocellulosic biomass;(iii) Providing a second solvent and combining with the material fromstep (ii), wherein at least some of the cellulose that is dissolved bythe first solvent in step (ii) precipitates out of the liquid phase;(iv) Providing a third solvent and combining with the material from step(iii), and then separating the substantially solid phase and blackliquor; and (v) Providing a fourth solvent and combining with thesubstantially solid phase from step (iv), and then separating the solidphase and light liquor.
 41. The process of claim 40, wherein the firstsolvent in step (ii) comprises one or more chemicals selected from thegroup consisting of hydrochloric acid, sulfuric acid, nitric acid,phosphoric acid, polyphosphoric acid, acetic acid, sulfur dioxide, zincchloride, sodium hydroxide, potassium hydroxide, ammonia, lithiumchloride/N,N-dimethylacetamide, 1-butyl-3-methylimidazoliumhexafluorophosphate, dimethylsulfoxide/tetrabutylammonium fluoridetrihydrate, N-methylmorpholine-N-oxide, cadmium monoxide/ethylenediamine(cadoxen), and water.
 42. The process of claim 40, wherein the secondsolvent in step (iii) comprises one or more chemicals selected from thegroup consisting of methanol, ethanol, 1-propanol, 2-propanol, acetone,propanal, 1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water.
 43. The process of claim 40, wherein the thirdsolvent in step (iv) comprises one or more chemicals selected from thegroup consisting of methanol, ethanol, 1-propanol, 2-propanol, acetone,propanal, 1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone),t-butanol, and water.
 44. The process of claim 40, wherein the fourthsolvent from step (v) comprises one or more materials selected from thegroup consisting of liquid water, steam, recycle water, processcondensate, fermentation-broth condensate, and carbon dioxide.
 45. Theprocess of claim 40, further comprising subjecting the black liquor,obtained in step (iv), to step (vi), a vapor/liquid separation operationselected from the group consisting of distillation, single-stageevaporation (flash), multiple-effect evaporation, thermocompression, andventuri scrubbing. 46-69. (canceled)
 70. The process of claim 40,wherein steps (ii)-(v) are each conducted in batches.
 71. The process ofclaim 41, wherein the first solvent in step (ii) comprisespolyphosphoric acid.
 72. The process of claim 42, wherein the secondsolvent in step (iii) comprises acetone. 73-87. (canceled)
 88. A processfor fractionating lignocellulosic biomass, the process comprising: (i)Providing lignocellulosic biomass; (ii) Providing polyphosphoric acidand combining with the lignocellulosic biomass, wherein thepolyphosphoric acid dissolves at least 90% of the cellulose present inthe lignocellulosic biomass; (iii) Providing acetone and combining withthe material from step (ii), wherein at least 90% of the cellulose thatis dissolved by the polyphosphoric acid in step (ii) precipitates out ofthe liquid phase; (iv) Providing acetone and combining with the materialfrom step (iii), and then separating the substantially solid phase andblack liquor; and (v) Providing water and combining with thesubstantially solid phase from step (iv), and then separating the solidphase and light liquor.
 89. The process of claim 88, further comprisingseparating the black liquor and recovering polyphosphoric acid.
 90. Theprocess of claim 89, wherein recovering polyphosphoric acid comprisesburning a process stream and recycling P₂O₅ and steam back to step (ii).91. The process of claim 88, further comprising recovering acetone fromthe black liquor, the light liquor, or both. 92-117. (canceled)